A nanny provides child care within the children's family setting. Traditionally, nannies were servants in large households and reported directly to the lady of the house. Today, modern nannies, like other domestic workers, may live in or out of the house, depending on their circumstances and those of their employers. There are many employment agencies that specialize in childcare.

Nannies differ slightly from others child care providers. A childminder works out of her own home, operating as a small business; depending on the country they live in, government registration may or may not be required, within the UK, a childminder must be Ofsted registered, hold a current paediatric first aid qualification, public liability insurance and follow the EYFS just like a nursery. A mother's helper, who may live in or out, assists the woman of the house with general chores as well as caring for the children. The term au pair usually refers to an untrained young woman (or occasionally man), who comes from abroad to live in the host family and learn the local culture and language, while helping with the children. A governess concentrates on educating children inside their own home, and a Kindergarten or schoolteacher does the same, but in a school environment.

In the 19th and early 20th century, the position was usually known as a "nurse", and was, as for many childcare jobs, invariably female. (Originally, the hired woman would have been expected to breastfeed the infant, a role known as a wetnurse.) In a great house (such as an English country house or town house), the nurse was a senior member of the household staff and ran her own domain, a suite of rooms called the nursery, supported by at least one assistant, known as a nursemaid (or nurserymaid). Because of their deep involvement in raising the children of the family, nannies were often remembered with great affection and treated more kindly than the junior servants. Nannies may have remained in the employment of the same aristocratic or gentry family for years, looking after successive generations of children.

Nannies were present in the households of the administrators of European colonial empires throughout the world. It was a characteristic feature of colonial society that the children of European administrative officers were entrusted to the care of native women.

Nannies in colonial times spent their lives in the homes of their masters, often from childhood till old age, taking care of more than one generation, depending on the duration of the post. It was not uncommon for these nannies to be brought along with the family away from their native country when administrative officers were posted "home" or to another colony.

A "live-in" nanny is much less common than it once was though still ideal for a woman or man looking to move interstate or abroad for either a short period of time or to set themselves up. Typically, a live-in nanny is responsible for the entire care of the children of their employers. This includes anything from washing the children's clothes and tidying the children's rooms, to supervising homework and preparing children's meals, as well as taking children to and from school and after-school sport and/or activities. The job may include a separate apartment (sometimes called a "nanny flat") and a car. While a live-in nanny was commonly available 24 hours a day in the past this is much less common now and often they are 10-12 hours on and the remainder of the day off (essentially while the children are awake and the parents are at work). A live-in nanny is nowadays more common amongst wealthier families, because of their possible flexibility while they live where they work. A live-in Nanny will have all her living expenses paid and provided by the employer.

A more recent addition to the role of the nanny is that of the night nanny. Sleep specialists or consultants typically work with older babies and children. The night nanny usually works with a family anywhere from one night to seven nights per week. A night nanny generally works with children from newborn to five years of age. A night nanny can provide a teaching role, helping parents to establish good sleeping patterns or troubleshooting the sleeping patterns of a child. Roles and qualifications vary between countries. The Night Nanny works together with the family's requirements and philosophies. The qualifications of a night nanny are usually in mothercraft nursing (see sleep guidance specialist or early childhood development). Pay rates vary from country to country but are usually well paid in comparison to the general nanny, as the night nanny is seen as a specialist or expert in their field.

Historically, European women were confined to their beds or their homes for extended periods after giving birth; care was provided either by her female relatives (mother or mother-in-law) or by a temporary attendant known as a monthly nurse. These weeks were called confinement or lying-in, and ended with the re-introduction of the mother to the community in the Christian ceremony of the churching of women. A modern version of this rest period has evolved, to give maximum support to the new mother, especially if she is recovering from a difficult labor and delivery.

In the US these specialty maternity nannies are known as Newborn Care Specialists (disassociating this specialty from medically qualified nursing). They are highly experienced in all aspects of newborns aside from medical issues. They might work 24 hours a day, seven days per week, but most work five nights/days a week for the first three months of a newborn's life. The role can consist of assisting parents with feeding guidance, nursery set up, premature infant, multiples, colic, reflux, and sleep guidance/training. There are various training organizations that offer non-accredited certifications, however, in an unregulated field parents should ensure that the qualifications of their maternity nanny are legitimate and accredited. The Newborn Care Specialist Association is one of many self-appointed certification entities. Some doulas specialize in postpartum care for mother and baby. Another related job is Perinatal assistant.

Chinese and related East Asian traditions practice a form of postpartum confinement known as zuo yue zi "sitting the month", traditions and customs regarding recovery from childbirth. The "confinement ladies" are referred to as yue sao,[2] and they have specialised knowledge of how to care for both baby and mother. In Singapore and Malaysia, newborn care specialists are better known as confinement nannies.[3] They assist the mother in taking care of the baby in order to let mother have a good rest. Confinement food will be prepared to help with the recovery. Usually, the employment period will be about 28 days up to a maximum of 16 weeks. In Korea these postpartum care workers are called Sanhujorisa.

In the Netherlands, standard postnatal care, supported by state medical insurance, includes more than a week of all-day visits called kraamzorg. This kraamverzorgster ("maternity home care assistant"[4]) teaches the new mother how to care for her baby, measures both of their health, prepares light meals, entertains older children, performs light household tasks, cleans the home and disinfects the bathroom.[5] She cares for the mother, baby, and family.

Typically, women from their 20s to 60s take up employment as nannies. Some are younger, though normally younger workers are nursemaids or au pairs rather than nannies in the traditional use of the term.

A few positions are filled by men; the term manny is sometimes used for a male nanny, especially in the US and UK.[6][7]

There are a number of national and international professional associations representing nannies and nanny agencies. The International Nanny Association (INA) was founded in 1985. INA is a non-profit organization which provides an educational association for nannies with placement, employment, and professional support. The Alliance of Professional Nanny Agencies (APNA) was founded in 1993. It is a non-profit organization that promotes professionalism in the nanny placement industry.
In June 2012 the Australian Nanny Association (ANA) was formed in Australia with the aims of having professional nannies included in the regulated government subsidized childcare scheme of the country. ANA is a volunteer run, not for profit association that also hopes to change some public misconceptions about nannies, encourage professionalism and be a source of support to nannies and the families who employ them.

In the United Kingdom, no formal qualifications or training are required to become a nanny. However, the National Nursery Examination Board (NNEB) was founded in 1945, as the awarding body in qualifications for childminders , and nursery personnel. In 1994 the NNEB and the Council for Early Years Awards (CEYA) merged to form CACHE – The Council for Awards in Children's Care and Education, with their CACHE Level 3 Diploma in Child Care and Education providing the knowledge and understanding of child development and education needed to work as a Nanny.

Norland College is a private college near Bath, which offers highly regarded training as a nanny. It also operates its own employment agency for graduates, as well as a local nursery in Bath.

In the United States, no formal qualifications are required to be a nanny [8]. Nannies in the United States can earn specialized Childcare Diplomas and Certifications from Amslee Institute. Amslee Institute offers 5 programs that are licensed by the Florida Department of Education, Commission of Independent Education, 5951. [9]. US Nannies also have access to online CACHE Endorsed Training created by 2004 International Nanny Association Nanny of the Year and parenting author Michelle LaRowe [10]. This training is offered through a partnership with NannyTraining.com and Nanny Stella, Inc., the only US Based CACHE Endorsed Training Centre for the early years [11].

Jo Frost, nanny who hosted a successful television program Supernanny in the UK and US, showing parents techniques to help with unruly children

Yoselyn Ortega, nanny accused of stabbing to death children Lucia and Leo Krim in 2012.

Sandra Samuel (b. 1964), an Indian nanny who saved the life of a child during the November 2008 Mumbai attacks in which the baby's two parents were murdered; later honored with honorary Israeli citizenship.

Charles (played by Scott Baio), a 19-year-old student and live-in babysitter in exchange for room and board, in the sitcom Charles in Charge

Daniel Hillard / Euphegenia Doubtfire (played by Robin Williams) a voice actor and father of three young children, in the movie Mrs. Doubtfire (1993)

Joseph Paul "Joe" Longo (played by Joey Lawrence), a former executive and commodities trader with an MBA who lost his job, money, and marriage and agrees to be the live-in nanny to assist his girlfriend, politician Mel, and give advice to her niece and nephew in the television series Melissa & Joey

Lieutenant Shane Wolfe (played by Vin Diesel), a United States Navy SEAL assigned to stay at the Plummer residence, to search for a secret project hidden somewhere in the house, and meanwhile to look after the family's five children, in the film The Pacifier (2005)